Mine's motive makes no sense

[друг (los siento)]

His entire story is "Nobody wants to be my friend so I joined the yakuza to make friends, but nobody wants to be my friend there too except Daigo,but now Daigo is in the hospital so now I gotta kill him :(( "

????

That makes no fkin sense

[Bankai9212]

Since I’m replaying this again, I’m trying to follow the plot, I know who the final boss is. Even as clunky as this game is, you don’t forget your first yakuza game.

[StaunchStache]

Just finished the game, so I hope this will make sense.
It's clear Mine is very emotionally stunted from his childhood as an unwanted orphan.

All his life has been spent clawing his way to success, valuing nothing but material gain. He's never had any experience seeing others as, well, human beings rather than tools or leeches he can't trust.

And then he found Daigo, who pretty much single-handedly wrecked his worldview by trusting him and treating him as a equal.

I think Mine became sort of emotionally dependant of Daigo in a way, which made him lose it entirely when he was shot. Suddenly the one person he trusted was completely unresponsive, barely better than a corpse.
His intent to kill Daigo could have been some way for him to rip the bandaid and get rid of all of those scary feelings once and for all, and go back to the "comfortable" way he lived his life up to that point (pursuing power/money endlessly).